Fully recharge typical over-the-counter alkaline batteries with a $0.50 circuit.
Parts list: 2 Resistors: 10-ohms and 1K ohms, 2 Diodes: 1N400x, 1 Transistor: Q1 2N3904 or equivalent NPN
See Afroman's guide to recharging alkaline batteries for diagrams and notes.
I've always fretted about the immense environmental and economic waste that goes along with batteries. Recharging Alkaline batteries isn't fusion in a jar, but it's pretty cool. I wonder if this is where all those 25c batteries on the subway come from. --dj